S. Jarosz et al. / Tetrahedron: Asymmetry 11 (2000) 1997±2006
2003
main trans-isomer: 1H NMR ꢀ: 6.94 (dd, J4,5=5.5, J5,6=15.8, H-5), 6.10 (dd, J4,6=1.5, H-6), 4.92
(J1,2=ꢁ0, H-1), 3.74 (CO2CH3), 3.36 (OCH3); 13C NMR ꢀ: 146.6 and 121.2 (CO), 106.4 (C-1),
81.8, 79.8 and 79.5 (C-2,3,4), 72.8 and 72.4 (2ÂCH2Ph), 55.6 and 51.6 (OCH3 and CO2CH3)}
according to the procedure described in Section 4.2.1.
1
Compound 32 (only trans). H NMR ꢀ: 5.92 (ddd, J5,6=14.9, J6,7a=8.8, J6,7b=8.5, H-6), 5.21
(dd, J4,5=8.3, H-5), 4.86 (J1,2=ꢁ0, H-1), 3.34 (OCH3); 13C NMR ꢀ: 135.2 and 124.4 (C-5,6),
105.6 (C-1), 82.8, 82.3 and 80.1 (C-2,3,4), 72.5 and 72.2 (2ÂCH2Ph), 54.9 (OCH3), 29.1, 27.3 and
9.2 [Sn(CH2)3CH3], 14.6 (C-7), 13.8 [Sn(CH2)3CH3]; HRMS m/z: 667.2789 [C34H52O4Na120Sn
(M+Na+) requires 667.2785].
4.3. Reaction of sugar allyltin derivatives with Lewis acids
The corresponding allyltin derivative (11, 15, 17, 24 or 32; 3 mmol each) was dissolved in
anhydrous methylene chloride (30 mL). A 2.0 M solution of ZnCl2 etherate in methylene chloride
(3 mL, 6 mmol) was added, the mixture was stirred at room temperature for 20 min, and partitioned
between ether (50 mL) and brine (30 mL). The organic layer was separated, washed with water,
dried and concentrated and the products were isolated by column chromatography (hexane:diethyl
ether, 7:1). Dienes 18 and 25 were characterized as acetates.
4.3.1. Methyl 2,3-di-O-benzyl-5,6,7,8-tetradeoxy-ꢁ-l-arabino-oct-5(E),7-dieno-1,4-furanoside 12
1H NMR ꢀ: 6.33 (m, H-6,7), 5.72 (dd, J4,5=7.8, J5,6=14.1, H-5), 5.19 (m, both H-8), 4.91 (d,
J1,2=1.3, H-1), 4.44 (m, J3,4=7.1, H-4), 4.00 (dd, J2,3=3.5, H-2), 3.78 (dd, H-3), 3.37 (OCH3);
13C NMR ꢀ: 136.0, 133.8 and 130.8 (C-5,6,7), 118.4 (C-8), 88.6, 87.5 and 81.3 (C-2,3,4), 72.3 and
72.0 (2ÂCH2Ph), 54.8 (OCH3); HRMS m/z: 389.1752 [C23H26O4Na (M+Na+) requires 389.1729].
4.3.2. 3-O-Benzyl-1,2-O-isopropylidene-5,6,7,8-tetradeoxy-ꢂ-d-xylo-oct-5(E),7-dieno-1,4-furanose8
13
When this compound was prepared by controlled decomposition of allyltin 15 only the trans-
isomer was detected in the NMR spectra.
1H NMR ꢀ: 6.36 (m, H-6,7), 5.95 (d, J1,2=3.8, H-1), 5.85 (dd, J4,5=7.5, J5,6=14.8, H-5), 5.20
(m, both H-8), 3.85 (dd, J3,4=3.1, H-3), 1.50 and 1.31 [C(CH3)2]; 13C NMR ꢀ: 136.1, 134.6, 127.1
(C-5,6,7), 118.2 (C-8), 111.4 [C(CH3)2], 104.7 (C-1), 83.4, 82.9, 80.8 (C-2,3,4), 72.0 (CH2Ph), 26.7,
26.1 [C(CH3)2].
When this product was obtained according to Narkunan and Nagarajan8 (see also Scheme 1)
additional signals, that could be connected with the cis-isomer, were seen in the 13C NMR spec-
1
trum at ꢀ: 133.0, 131.7, 125.0 (C-5,6,7), 119.8 (C-8), and 112.1 [C(CH3)2]. Also, in the H NMR
spectrum the H-3 resonance split into two signals at ꢀ: 3.89 (the minor cis-isomer) and 3.85
(the main trans-isomer). Integration of these signals allowed us to estimate the trans:cis ratio at
9:1.
4.3.3. 1-O-Acetyl-3-O-benzyl-1,2-O-isopropylidene-4,5,6,7-tetradeoxy-4(E),6-dieno-d-erythro-heptose
18-Ac
1H NMR ꢀ: 6.36 (m, H-5,6), 6.22 (d, J1,2=2.3, H-1), 5.65 (dd, J3,4=7.7, J4,5=14.5, H-4), 5.21
(m, H-7), 4.23 (dd, J2,3=6.2, H-2), 3.87 (dd, H-3), 2.07 (COCH3), 1.47 and 1.46 [C(CH3)2]; 13C
NMR ꢀ: 170.1 (CO), 135.9, 135.8 and 129.0 (C-4,5,6), 118.7 (C-7), 112.9 [C(CH3)2], 96.6 (C-1),
83.6 and 78.8 (C-2,3), 70.5 (CH2Ph), 27.2 and 26.7 [C(CH3)2], 21.2 (COCH3).